Salivary Gland Development PDF

 SALIVARY GLAND DEVELOPMENT All Major SG - oral ectoderm @ 4-8 week of IU life. Minor SG - Oral ectoderm - develop after the major SG. Stage–2 Cord growth Stage- 1 Bud formation A solid...

 SALIVARY GLAND DEVELOPMENT All Major SG - oral ectoderm @ 4-8 week of IU life. Minor SG - Oral ectoderm - develop after the major SG. Stage–2 Cord growth Stage- 1 Bud formation A solid cord of cells forms due to continued proliferation of bud Proliferation of oral epithelium into underlying ectomesenchyme. forming focal thickening.  STAGE 3 Branching in Cords The epithelial cord proliferates rapidly and branches into terminal bulbs (presumptive acini). Stage – 4 Lobule formation The branching continues at terminal portions of the cord, forming extensive tree- like system of bulbs. Stage 5 C a n a l i z a t i o n o f cords Stage 6 Cyto-differentiation Canalization of the epithelial Mitotic activity shifts to terminal bulb cord -hollow tube or duct – (stem cells)-differentiation into acinar Lumen. cells, duct cells & Myoepithelial cells. After development of lumen in terminal buds the epithelium consists of 2 layers of cells. ❑ Inner layer > secretory cells - mucous / serous ❑ Some cells of outer layer > myoepithelial cells Capsule forms from ecto-mesenchyme and surrounds the entire gland.. 5 partitions of CT –septa, continuous with capsule are formed. nerves & blood vessels supplying the gland run within these septa, Septa also divides the gland into lobes and lobules. 6 7  DUCTAL SYSTEM Central lumen of acini continue via a fine series of ducts which constantly merge with each other and grow larger eventually to merge into the main excretory duct. These ducts comprise the ductal system. 8 The main excretory duct which empties into the oral cavity, divides into: ▪ Interlobar & Interlobular excretory ducts that enter the lobes and lobules of the gland. The predominant intralobular ductal component is - striated duct. 9 10 The lumen of the end piece is continuous with that of the intercalated duct. 11  STRUCTURE OF TERMINAL SECRETORY UNITS The basic functional unit of a SG is the terminal secretory unit called acini which is made up of epithelial secretory cells, namely serous & mucous cells. The serous, mucous along with myoepithelial cells are arranged in an acinus with a central lumen. The cells in the acini are arranged in a single layer & rest on basement membrane. 12 13  SEROUS ACINUS The secretory end pieces that are composed of serous cells are typically spherical & consist of 8 –12 Cells surrounding a central lumen. the central lumen may have a star-shaped morphology because of extension of lumen in between the cells called Intercellular canaliculi.(ICC) 14 15  MUCOUS ACINUS secretory end pieces that are composed of mucous cells typically have tubular configuration; In CS, tubules appear as round profiles with mucous cells surrounding a central lumen of larger size. intercellular canaliculi- Absent. 16 17  mucous end pieces in major SGs & some minor SGs have serous cells associated with them in the form of a demilune or crescent or bonnet covering the mucous cells. presence of demilunes is questioned in recent studies. Could be result of artifact during tissue preparation.. 18 19  HISTOLOGY OF SALIVARY GLAND  Acinar units  Serous cells  Mucous cells  Myoepithelial cells  Ductal units  Intercalated duct  Striated duct  Terminal/excretory duct  Connective tissue  SEROUS CELLS Shape- Pyramidal, Narrow apex near lumen. Spherical nuclei located basal 1/3rd broad base adjacent to the CT stroma & narrow apex forming part of the lumen of the end piece. Intercellular canaliculi – Present. 21  Numerous secretory granules ( ~ 1µm) - Zymogen granules are present in the apical cytoplasm. They have distinct limiting membrane. In general, serous cells produce proteins and glycoproteins – They have well-defined enzymatic, antimicrobial, calcium binding activities. Typically, serous glycoproteins have N-linked oligosaccharide side chains. 22  Basal cytoplasm contains numerous RER, which converge on a large Golgi complex located just apical or lateral to nucleus. Forming secretory granules of variable size and density are present at trans face of golgi complex. Contain - cytoskeletal components, mitochondria, lysosomes & peroxisomes. 23  TEM- SEROUS CELL Extensive RER – parallel aggregates – lateral & basal to nucleus. Golgi located apical to nucleus secretory granules smaller- at apical area – covered by unit membrane. 24 Plasma membranes exhibit several specializations. Luminal surface - studded with a short microvilli. Lateral surfaces have occasional folds that interdigitate with adjacent cells. Basal surface thrown into regular folds. These specializations increases the surface area of cell. 25 Small lumen Apical cytoplasm- secretory granules Prominent nuclei. 26 MUCOUS CELLS Shape- Pyramidal, Apex – wider than Serous cell Flattened nucleus at base Intercellular canaliculi- Absent. 27 Main products of mucous cells are mucins (glycoprotein) with O-linked oligosaccharide chains. Prominent feature – accumulation large amounts of secretory product (mucus) in the apical cytoplasm - compresses the nucleus and ER against the basal cell membrane. 28  Mucous cells have a large golgi complex, located mainly basal to the mass of secretory granules. Small granules form at trans face of the golgi complex, increase in size, and join the rest of the granules stored in apical cytoplasm. ER & most other organelles are limited mainly to basal cytoplasm of cell. 29  Secretory material appears unstained in routine histologic preparations-empty appearance to the supranuclear cytoplasm. Nucleus- flattened / not conspicuous. Lumen- Bigger 30  Special stains such as the Periodic acid– Schiff stain (PAS) or alcian blue-Mucus is strongly stained. 31 TEM- MUCOUS CELL Prominent golgi complex – located b/w nucleus and secretory droplets. secretory granules are irregular and larger than serous. membranes are disrupted- often fused. 32  Filled with secretory granules; Nuclei compressed in basal area. 33 34